The present invention is directed to a device for moistening the inlet air of a combustion engine operating with air suction and having a cooling water circuit.
It is known to moisten the inlet air of Diesel engines provided with turbo-supercharges in order to reduce the NOx portion in the exhaust gas in this manner. Such a method with a corresponding device is described in WO 95/23286. In this system, a moistening means is used which is traversed by the inlet air and water, wherein the inlet air is compressed prior to the moistening and the energy inherent in the cooling water or the exhaust gases of the combustion engine is used for preheating the water before the same is introduced into the moistening means.
The present invention is directed to internal combustion engines operating with air suction, i.e. without a turbosupercharger.
It is the object of the invention to provide a device for moistening the inlet air of a combustion engine operating with air suction by means of which a NOx reduction in the exhaust gas of the combustion engine can be achieved in an especially simple manner at an especially low cost.
This object is attained by a device for moistening the inlet air of a combustion engine operating with air suction and having a cooling water circuit, said device comprising.
a moistening means for the inlet air through which the inlet air and the moistening liquid flow in contact with one another, and
an air/water heat exchanger or air/air heat exchanger serving for the preheating of the inlet air, disposed upstream of the moistening means and traversed by the cooling water or by the exhaust gas of the combustion engine and by the inlet air.
The invention is particularly directed to Diesel engines or gas engines which, however, does not exclude the use of the invention with other combustion engines.
A plurality of old combustion engines which are in operation do not have turbo-superchargers but generate exhaust gases having a relatively high NOx portion. This is especially true for smaller Diesel engines of ships, boats, generators etc. Since in many cases these combustion engines were constructed with the intent to use them at a maximum capacity the NOx emissions are high. Normally, such combustion engines have a cooling circuit in which water (fresh water) circulates.
The present invention emanates from the principle of preheating the inlet air for the combustion engine, namely by utilization of the thermal energy inherent in the cooling water or the exhaust gas of the combustion engine, and thereafter to moisten the preheated inlet air. The thermal energy inherent in the cooling water is transferred to the inlet air by means of an air/water heat exchanger. The inlet air is heated to a temperature of 60-70xc2x0 C. which represents an ideal temperature range for the following moistening step. Addition of moisture of about 30 g per kg dry air can be obtained in a simple manner without great cost in order to substantially reduce the NOx formation in the exhaust gas.
The preheated inlet air entering the moistening means is moistened by the moistening liquid and cooled within the same. Preferably, the moistening means is used as described in the above-mentioned WO 95/23286 (U.S. Pat. No. 5,758,606) or in the non-published German patent application 197 50 181.8 wherein an opposite flow, cross flow and/or parallel flow of the media is possible.
Preferably the air/water heat exchanger and the moistening means are disposed upstream of the air filter of the combustion engine. By this, the real air filter is less loaded. Of course, a location of the air/water heat exchanger and the moistening means downstream of the air filter is also possible.
Another embodiment of the invention which is especially used with Diesel engines of ships is characterized by the feature that the moistening liquid is normal salt water (sea water). Normally, such Diesel engines on ships are associated with a sea water circuit which is used for cooling the cooling water of the Diesel engine by means of a heat exchanger wherein the cooling water is normally fresh water. Now, according to the invention salt water can be taken from the existing salt water circuit and can be fed to the moistening means. In the same the salt water is contacted with the preheated inlet air in order to moisten the inlet air. The salt water leaving the moistening means again can be discharged or recirculated into the supply line of the moistening means again. With this embodiment according to which the salt water for moistening is taken from a present salt water circuit serving for cooling the cooling water, the salt water is slightly heated by the thermal energy transferred from the cooling water of the combustion engine so that slightly preheated salt water in the moistening means contacts the preheated air.
Of course, the salt water need not be taken from an existing salt water circuit. The moistening water can be taken directly form the sea (with ships, boats) as well.
The above-described embodiment has the advantage that no additional fresh water is required for the moistening, thereby avoiding additional expense, especially on ships. Of course, this does not exclude the normal use of fresh water (river water).
With the inventive solution the moistening of the inlet air is carried out adiabatically.
If, according to the invention, the exhaust gas of the combustion engine is used for preheating the inlet air and an air/air heat exchanger is used the exhaust gas or a part thereof can directly flow through the air/air heat exchanger. However, for instance, the exhaust gas can also pass a second heat exchanger in which air is heated which is fed to the air/air heat exchanger for heating the inlet air and is recirculated from there to the heat exchanger traversed by the exhaust gas. Also in this manner the existing energy is utilized for preheating the inlet air. Moreover, the same is true for the preheating by means of the cooling water.
According to the invention an intended heating of the moistening medium (water) is not carried out.
According to another embodiment of the invention a plurality of air/water or air/air heat exchanger/moistening units are disposed one behind the other in flow direction of the inlet air. With this embodiment an especially exact control of the amount of the admission of moisture of the inlet air can be carried out, for example, in respect to the actual water temperature.
Preferably, the device according to the invention has means for separating the foreign particles entrained by the inlet air. Such a means is used especially if salt water is used as moistening medium.